The present invention relates to a shutoff device for pulverized coal burners of a pulverized coal furnace.
In steam generators, the furnace of which is equipped with two or more pulverized coal burners, burners that are shut down during the operation of a steam generator are supplied with cooling air via the combustion air supply lines (secondary air, tertiary air) to protect the burner nozzles from being thermally overstressed. The primary tube of the pulverized coal burners, via which the introduction of fuel is effected during the operation, do not have cooling air flow therethrough when burners are not in operation.
In conformity with all applicable regulations relative to the equipping and operation of pulverized coal furnaces or steam generators in which pulverized coal is injected into the combustion chamber via two or more burners, and which are supplied with pulverized coal from two or more parallel fuel systems, the pulverized coal supply line must be provided with shutoff devices that are reliably opened during the operation of the pertaining supply systems, and after the pertaining fuel supply device is turned off must be closed. This is generally realized with shutoff mechanisms where a shut-off plate is inserted into the cross-section of the pertaining supply lines perpendicular to the axis of flow by an automatically and/or manually actuated drive means. As a result, the complete blocking of the corresponding fuel supply paths is effected. In this state, there is no flow-through of the fuel paths and hence also no cooling of the pulverized coal burner nozzles.
Due to the lack of flow-through, and due to the pressure and velocity conditions in the combustion chamber of the pulverized coal furnace, hot combustion gases can re-circulate into the fuel nozzles of the turned-off burners. Especially with modern NOxxe2x80x94poor pulverized coal burners, where the position of the fuel nozzles is shifted as far as possible in the direction of the combustion chamber, the high irradiation effects an intensive increase in temperature in the material of the burner nozzles. As a consequence of the irradiation and the lack of flow-through a premature failure or destruction of the pulverized coal nozzles can occur due to thermal overstressing of the material.
It is therefore an object of the present invention to provide a closed system for the cooling of the pulverized coal supply path within a pulverized coal burner via an air stream without in so doing adversely affecting the necessary safety device, namely the blocking or closing off of the pulverized coal supply path.